I. SPECIAL COLLECTIONS. 37 



181. King's Pressure Gauge, showing mechanical pressure 

 of gas or air. Constructed by Mr. Sugg. 



Standards Department, Board of Trade. 



The amount of the mechanical pressure of gas or air contained in a gas- 

 holder is shown by this pressure gauge, when it is put in communication 

 with the gasholder by an air-tight tube. The surface of the water in the 

 cistern of the pressure gauge is depressed by the force of the gas or air, and 

 alters the level of a metal cup floating on it. A cord is attached to the float, 

 and passes over a pulley, the spindle of which, aided by friction rollers, 

 carries a pointer moving on a graduated dial, and thus indicates the amount 

 of pressure in hundredths of an inch. 



Specimens of Standard Weights and Measures. 



182. Copy of Standard Weight, 112 Ibs., of Queen 

 Elizabeth. 



One of two similar bronze weights deposited in one of the old Treasuries of 

 the Exchequer, and fully described in App. IV. to the 7th Annual Report of 

 the Warden of the Standards. 



183. Gilt Steel Yard, line measure, of the same form as the 

 imperial standard yard. Constructed by Troughton and Simms. 



Well-holes are cut down to the mid-depth of the bar, where the defining 



lines are cut upon gold studs, thus rfflrj )>the measure being taken 



at the middle portion of the central transversal line, intercepted between the 

 two longitudinal lines. These lines, including the two transversal guide lines, 

 one on each side of the defining Hue, are 0* 01 inch apart. 



184. Steel Yard End Measure, showing the form of end- 

 standard yard adopted by the Standards Commission. Con- 

 structed by Troughton and Simms. 



The form of the defining ends is that of a spherical surface, whose centre is 

 the centre of the division line in the middle of the bar's length. The material 

 of the defining end is a highly polished plug of agate, shrunk into a slightly 

 conical hole at the end of the steel bar. 



185. Steel Foot End- Measure. Constructed by Troughton 

 and Simms. 



186. Two Steel 6-inch End-Measures, one finished and 

 one unfinished. Constructed by Troughton and Simms. 



187. A 10-Foot Measuring Rod, of pine wood, bound 

 with brass. Constructed by Troughton and Simms. 



188. A 3 -Foot Measuring Bod, of pine wood, bound with 

 brass. Constructed by Troughton and Simms. 



